Method of insulating sheet metal.



WILLIS R. WHITNEY,

OF SOHENEOTADY, NEW YORK, ASSIGNOR TO GENERAL ELEOTRIO COMPANY, A CORPORATION OF NEW YORK.

METHOD OF INSULATING SHEET METAL.

Specificationof Letters Patent.

Patented June 1, 1909.

Application filed February 28, 1907. Serial No. 359,910.

To all whom it may concern:

Be it known that I, WILLIS R. WHITNEY, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Methods of Insulating Sheet Metal, of which the following is a specification.

Transformer iron and various other sheet metal parts employed in electrical apparatus require an insulating coating to prevent the passage of electrical energy from one sheet to another. In general, this insulation must be thin and must maintain its insulating 1'5 qualities when heated considerably above room temperature, and furthermore it must. be of such a plastic and tenacious nature as to resist flaking or cracking when the metal sheet is bent.

My present invention com rises a method of applying a thin coating 0 insulating material having the properties above referred to and being otherwise suitable for use in electrical apparatus.

According to my invention the sheets of metal are coated with a colloidal suspension of an organic gum and then treated to drive out the fluid of the suspension and liquefy the gum to produce a smooth coherent coating on the sheet. Gum copal is a suitable organic gum for use according to my process. To produce a colloidal suspension of gum copal, I grind copal chips and water in a ball mill until the copal reaches such a fine degree of subdivision that it remains in suspension. The proportion of copal to water may vary through a considerable range, but

I contemplate the use of a solution containing twenty or less per cent. of copal by When the suspension comes from the ball mill, it is likely to contain a great quantity of small air bubbles. These give it a consistency about like that of whipped cream.

, weight.

Such a suspension is not altogether suited for my purpose as the air bubbles are likely to produce defects on a plate treated with the solution. I find that the suspension can be clarified by the addition ofa small quantity of salts, such as barium hydrate, aluminum chlorid, or barium chlorid. A few drops of a 10% solution of any of the above is suflicient for each gallon of the suspension.

These salts cause precipitation of the copal and liberation of t 1e air bubbles. After the solution has once been rendered free from air it may be stirred and W111 agam become a uniform and practically permanent suspenslon.

In order to insure against possible precipitation of the solution when used commercially on a large scale, I may, if desired, add a small quantity of sodium hydrate.

The suspensionwhen in normal condition has about the consistency of milk and is therefore in suitable condition for application to the sheet metal by spraying, dipping, 'or by means of rollers between which the metalis passed. I prefer to use the dipping process as I find that the results are satisactory and the process is entirely suitable for commercial application.

After a sheet metal plate, such as a transformer lamination, has been dipped in the suspension, it is'drained for a moment to remove the excess solution and is then placed on a suitable carrier and conveyed through an oven where the temperature is raised to between 100 and 200 degrees C. This first drives the water from the iron and then melts the gum into a thin adherent coating. As the vaporizable components of the susension consist principally of water, the urnace treatment is entirely free from the dangers which attend processes employing inflammable solvents such as alcohol or turpentine. The finished iron is somewhat green in color and has a smooth, glossy ap earance. The coating of insulating materia is very thin and uniform throughout the plate. The plate may be bent without causing the coating to crack or separate from the metal.

What I claim as new and desire to secure by Letters Patent of the United States, is,

1. The process which consists in coating a sheet metal plate with a colloidal suspension of gum copal, and then heating said plate to produce a uniform adherent coating of gum copal.

2. The process which consists in treating a conductor with a suspension of gum copal in water and then baking said conductor to remove the water and melt the copal into a homogeneous coating.

3. The process which consists in coating a metal with a colloidal suspension of an organic gum and then heating said metal to evaporate the liquid of the colloid and melt the residue into a thin homogeneous film.

4. The process which consists in grinding metal plates, and baking said plates to evaporate the water and melt the copal into a homogeneous film.

6. As a coating bath, a colloidal suspension of gum copal in water.

In witness whereof, I have hereunto set my hand this 26th day of February, 1907. WILLIS R. lVHlTNEY.

an organic gum with water to produce a substantially permanent suspension, coating a sheet metal plate with said suspension, removing the water therefrom, and baking to produce a homogeneous film of gum on said plate.

5 The process which consists in grinding guin copal with water to produce a colloidal suspension, precipitating with a salt to remove air bubbles from the suspension, ap- F plying the product thereby obtained to itnesses BENJAMIN B. HULL, HELEN ORFORD. 

